Recently, researches on hybrid type construction equipment, which improves fuel efficiency by storing surplus power of an engine in a battery, and supplying power from the battery to the engine having insufficient power so as to cope with a rapid increase in oil price, are being actively conducted.
A system, which uses the engine and an electric motor as a common power source as described above, and has an electrical energy storage device, is referred to as a hybrid system. For example, as the hybrid system, there is a hybrid system for heavy equipment such as a hybrid vehicle, and an excavator.
Meanwhile, a general excavator system uses an engine as a power source and serves to swing or move a boom, an arm and a bucket, which are final loads, by means of hydraulic pressure. On the contrary, in the case of a hybrid excavator system, a motor and an electricity storage device are additionally installed in a general excavator, thereby improving overall efficiency of the excavator system.
FIG. 1 is a configuration diagram of a hybrid excavator in which a swing apparatus is driven by electricity by being separated from a hydraulic power train system in the related art.
As illustrated, a swing motor 70 is driven by being supplied with electrical energy from an energy storage device 60, and the energy storage device 60 is supplied with electric power from an engine auxiliary motor 20. In a situation in which the swing motor 70 decelerates, kinetic energy of the swing apparatus is regenerated to the energy storage device 60, and regarding electric power that is lost due to friction and the like, the engine auxiliary motor 20 supplies electric power to maintain a voltage of the energy storage device 60 at an appropriate level. Meanwhile, an engine 10, a pump 30, a control valve 40, and a boom/arm/bucket traveling operator 50 are the same components as those provided in an engine type excavator in the related art.
A method of charging an energy storage device 60 of an electric hybrid construction machine in the related art is performed by dividing a voltage of the energy storage device 60 into regions that may be charged and discharged, and charging the energy storage device 60 with a predetermined target voltage independently of an operational situation of an actuator. Therefore, when supplying the same output to the actuator in a working mode in which a voltage of the energy storage device 60 is maintained at a low level, it is necessary to supply a large amount of current, and as a result, an electrical copper loss significantly occurs in proportion to the square of the current.
Meanwhile, in a working mode in which a voltage of the energy storage device 60 is maintained at a high level, regenerable energy of the swing motor 70 cannot be stored in the energy storage device 60, and the regenerable energy is radiated as thermal energy through heat generating resistant elements and the like, such that a loss of energy occurs, and as a result, fuel efficiency of the electric hybrid construction machine deteriorates. In a case in which a capacity of the energy storage device 60 is designed to be larger than necessary in order to prevent the above problem, high costs are incurred, and there is a restriction in designing the energy storage device 60 because the energy storage device 60 occupies a large volume when the energy storage device 60 is mounted in a vehicle.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.